In the cable making industry, extruders are used for forming a sheath or casing of plastic material about a cable core, more particularly made from metal. These extruders comprise an extrusion head disposed at right angles with respect to the axis of the hopper which supplies this head with material to be extruded, the head having passing longitudinally therethrough the core of the cable to be covered and having at one of its ends a die for obtaining the desired sheath profile.
In some cases, the die is mounted for rotation with respect to the extrusion head, more especially for manufacturing cables with helical grooves intended to receive optical fibers. Usually, the die is driven from a mechanism disposed in the immediate vicinity of this die.
This arrangement has a number of drawbacks. It does not allow the operator to readily fit or remove the die, since the drive mechanism limits access thereto. It is not possible to heat the die, since the drive mechanism is not, a priori, capable of supporting over heating: it follows then that the plastic materials which may be extruded are limited to those with a low melting point. Furthermore, it is difficult to provide and control the seal between the rotating die and the fixed body of the extrusion head, because of the high pressures of the plastic material upstream of the die.
Therefore, one of the aims of the present invention is to provide a rotary extrusion head, more especially for manufacturing cables with helical grooves for optical fibers, which allows ready access to the die and which may be heated if required.
Another aim of the invention is to provide an extrusion head allowing the mechanical part driving the die to be cooled without affecting the temperature of the product being extruded.